Power amplifier and radio communication device using the amplifier

ABSTRACT

A power amplifier includes amplifier elements to amplify input signals of different frequencies. The amplifier also includes a power supply circuit that includes a common power supply path including an end connected to a power supply input terminal connected to a DC power supply. The amplifier further includes individual power supply paths each including an end connected to the other end of the common power supply path, and the other end connected to the main electrode of a corresponding one of the amplifier elements. The individual power supply paths have different impedances.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based upon and claims the benefit of priorityfrom prior Japanese Patent Application No. 2003-147917, filed May 26,2003, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a power amplifier mainly for ahigh-frequency band, and more particularly to a power amplifier thatselectively amplifies a plurality of input signals of differentfrequencies.

[0004] 2. Description of the Related Art

[0005] There exist radio communication systems for providing services ofmobile communication of a plurality of frequency bands. In such systems,radio communication devices, such as mobile terminals, are generallyprovided with the same number of transmission signal power amplifiers asthat of frequency bands used.

[0006] For instance, in the personal digital cellular (PDC) system thatuses two frequency bands, two power amplifiers for the 800-MHz band and1900-MHz band are provided in a single mobile terminal. Even a mobileterminal compatible with different systems, such as an 800-MHz-band PDCand 1900-MHz-band personal handy-phone system (PHS), is provided withpower amplifiers dedicated to respective frequency bands.

[0007] In a radio communication device, such as a mobile terminal usinga plurality of frequency bands, it is difficult to satisfy a demand forsize reduction if power amplifiers dedicated to the respective frequencybands.

[0008] On the other hand, broadband amplifiers for use in measuringdevices can amplify signals of different frequency bands. This type ofamplifier, however, consumes much power, therefore is not suitable formobile terminals that use a battery as a power supply. For this reason,they are not used in mobile terminals.

BRIEF SUMMARY OF THE INVENTION

[0009] It is an object of the invention to provide a power amplifier forselectively amplifying signals of different frequency bands, which canbe made compact, and a radio communication device using the poweramplifier.

[0010] According to an aspect of the invention, there is provided apower amplifier comprising: a first amplifier element configured toamplify a first input signal of a first frequency, the first amplifierelement including a first input terminal which receives the first inputsignal, and a first output terminal which outputs a first output signalobtained by amplifying the first input signal; a second amplifierelement configured to amplify an input signal of a second frequency, thesecond amplifier element including a second input terminal whichreceives the input signal of the second frequency, and a second outputterminal which outputs a signal obtained by amplifying the input signalof the second frequency; a power supply input terminal connected to adirect-current power supply; a common power supply path including an endconnected to the power supply input terminal, and another end; a firstindividual power supply path including an end connected to the anotherend of the common power supply path, and another end connected to thefirst output terminal, the first individual power supply path having afirst impedance; and a second individual power supply path-including anend connected to the another end of the common power supply path, andanother end connected to the second output terminal, the secondindividual power supply path having a second impedance.

[0011] According to another aspect of the invention, there is provided apower amplifier similar to the above but further comprising: a firstoutput matching circuit connected to the first output terminal of thefirst amplifier element; and a second output matching circuit connectedto the second output terminal of the second amplifier element.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0012]FIG. 1A is a block diagram of a power amplifier according to afirst embodiment of the invention;

[0013]FIG. 1B shows a FET used for each amplifier element in FIG. 1A;

[0014]FIG. 1C shows a bipolar transistor used for each amplifier elementin FIG. 1A;

[0015]FIG. 2 is a diagram useful in explaining the impedancerelationship between components in the first embodiment, assumed when anf1 amplifier element is operating;

[0016]FIG. 3 is a diagram useful in explaining the impedancerelationship between components in the first embodiment, assumed when anf2 amplifier element is operating;

[0017]FIG. 4 illustrate the configuration of a power amplifier accordingto a second embodiment of the invention;

[0018]FIG. 5 is a diagram useful in explaining the impedancerelationship between components in the second embodiment, assumed whenan f3 amplifier element is operating;

[0019]FIG. 6 shows a first structure example of a power supply circuitincorporated in the first embodiment;

[0020]FIG. 7 shows a second structure example of the power supplycircuit incorporated in the first embodiment;

[0021]FIG. 8 shows a third structure example of the power supply circuitincorporated in the first embodiment;

[0022]FIG. 9 shows a fourth structure example of the power supplycircuit incorporated in the first embodiment;

[0023]FIG. 10 shows a fifth structure example of the power supplycircuit incorporated in the first embodiment;

[0024]FIGS. 11A and 11B are schematic diagrams illustrating front andback specific structure examples of the power amplifier of the firstembodiment;

[0025]FIGS. 12A, 12B and 12C are schematic diagrams illustrating pluralside specific structure examples of a power amplifier according to athird embodiment;

[0026]FIG. 13 is a block diagram of a multi-stage power amplifieraccording to a fourth embodiment; and

[0027]FIG. 14 is a block diagram of a radio communication deviceaccording to a fifth embodiment.

DETAILED DESCRIPTION OF THE INVENTION FIRST EMBODIMENT

[0028]FIG. 1A shows the configuration of a power amplifier according toa first embodiment of the invention. The first embodiment will bedescribed using, as an example, a power amplifier operable at twofrequencies f1 and f2.

[0029] The power amplifier has input terminals 11 and 12 for receivinginput signals Vi1 and Vi2 of frequencies f1 and f2. The input signal Vi1is input to the input terminal of an f1 amplifier element 17 via aninput matching circuit 14. The input signal Vi2 is input to the inputterminal of an f2 amplifier element 18 via an input matching circuit 15.The signal amplified by the amplifier element 17 is output as an outputsignal Vo1 from an output matching circuit 21. Similarly, the signalamplified by the amplifier element 18 is output as an output signal Vo2from an output matching circuit 22.

[0030] The amplifier elements 17 and 18 are formed of, for example, theFET as shown in FIG. 1B, or the bipolar transistor as shown in FIG. 1C.Further, each of the amplifier elements 17 and 18 is not always formedof a single transistor, but may be formed of, for example, twotransistors connected in series. In FIG. 1A, reference numerals 1, 2 and3 denote the control electrode and first and second main electrodes ofthe amplifier element 17. If the element 17 is formed of a FET, its gateelectrode G, drain electrode D and source electrode S correspond to thecontrol electrode and first and second main electrodes, respectively.Further, if the element 17 is formed of a bipolar transistor, its baseelectrode B, collector electrode C and emitter electrode E correspondthe control electrode and first and second main electrodes,respectively.

[0031] The signals output from the input matching circuits 14 and 15 areinput to the respective control electrodes 1 of the amplifier elements17 and 18. The signals amplified are output from the respective firstmain electrodes 2 of the amplifier elements 17 and 18. The second mainelectrodes 3 of the amplifier elements 17 and 18 are connected to aconstant potential point (not shown), for example, grounded.

[0032] The supply of power, i.e., a DC voltage, to the amplifierelements 17 and 18 is performed by a power supply circuit describedbelow. Firstly, one end of a common power supply path 31 is connected toa power supply input terminal 30 that is connected to a DC power supplyVcc. The common power supply path 31 is connected to both the amplifierelements 17 and 18. The other end of the common power supply path 31 isconnected to one end of each of individual power supply paths 32 and 33dedicated to the amplifier elements 17 and 18, respectively. The otherends of the lines 32 and 33 are connected to the respective first mainelectrodes of the amplifier elements 17 and 18. As described later, theindividual power supply paths 32 and 33 have different impedances.

[0033] The operation of the power amplifier of the first embodiment willbe described.

[0034] The f1 and f2 amplifier elements 17 and 18 operate at differentfrequencies f1 and f2, as described above. However, they are controlledsuch that they operate exclusively. In other words, when one of theelements 17 and 18 is operating, the other is kept inoperative.

[0035] The output matching circuit 21 matches impedances with a circuit(not shown) connected after it, when the f1 amplifier element 17 isoperating at the frequency f1. The circuit 21 has a conjugate impedanceZ_(P1ON)* with respect to the output impedance Z_(P1ON) of the amplifierelement 17 during operation. Similarly, the output matching circuit 22matches impedances with a circuit (not shown) connected after it, whenthe f2 amplifier element 19 is operating at the frequency f2. Thecircuit 22 has a conjugate impedance Z_(P2ON)* with respect to theoutput impedance Z_(P2ON) of the amplifier element 18 during operation.

[0036] The output matching circuits 21 and 22 do not necessarily haveconjugate impedances with respect to the output impedances of theamplifier elements 17 and 18 during operation. They may be adapted todifferent purposes. For instance, the impedances of the output matchingcircuits 21 and 22 may be set so that the output signals Vo1 and Vo2have the maximum levels and/or the minimum distortion values.

[0037]FIG. 2 shows the impedances of the components of FIG. 1A assumedwhen the input signal Vi1 of the frequency f1 is input to the inputterminal 11, and the f1 amplifier element 17 is operating and the f2amplifier element 18 is not operating. The operating amplifier element17 has the output impedance Z_(P1ON). The first main electrode (outputterminal) of the amplifier element 17 is connected to the outputmatching circuit 21 having the conjugate impedance Z_(P1ON)* withrespect to Z_(P1ON), and is also connected to the power supply circuit.The power supply circuit has the common power supply path 31 andindividual power supply paths 32 and 33, as described above. DC power issupplied to the f1 amplifier element 17 from the input terminal 30 viathe common power supply path 31 and individual power supply path 32.

[0038] On the other hand, the f2 amplifier element 18, which is notoperating, has an output impedance Z4. The impedance Z5 of the outputmatching circuit 22 connected to the first main electrode (outputterminal) of the amplifier element 18 is identical to the conjugateimpedance Z_(P2ON)* with respect to the output impedance Z_(P2ON) of theamplifier element 18 during operation.

[0039] Assuming that the synthesis impedance when the power supplycircuit is viewed from the first main electrode of the operating f1amplifier element 17 is Za, Za is given by $\begin{matrix}{Z_{a} = \frac{{Z_{1}\left( {Z_{3} + \frac{Z_{4}Z_{5}}{Z_{4} + Z_{5}}} \right)} + Z_{2}}{Z_{2}\left( {Z_{1} + Z_{3} + \frac{Z_{4}Z_{5}}{Z_{4} + Z_{5}}} \right)}} & (1)\end{matrix}$

[0040] where Z1 represents the impedance of the common power supply path31, Z2 and Z3 represent the impedances of the individual power supplypaths 32 and 33, and Z2≠Z3. The impedances Z1, Z2 and Z3 are expressedas a frequency function, Zn(f)=Rn(f)+Xn(f) (n=1, 2, 3). Rn(f) representsthe resistance component, and Xn(f) the reactance component. In equation(1) directed to the case where the input signal Vi1 of the frequency f1is input to the input terminal 11, and the f1 amplifier element 17 isoperating, Z1, Z2 and Z3 are Z1(f1), Z2(f1) and Z3(f1), respectively.

[0041] At this time, if the real part Re{Za} of the synthesis impedanceZa is set higher than the real part Re{Z_(P1ON)*} of the impedanceZ_(P1ON)* of the output matching circuit 21, as shown in the followingformula (2), the output signal (high frequency power) of the amplifierelement 17 is efficiently guided to the output side via the outputmatching circuit 21, and output as the output signal Vo1.

Re{Z _(a) }>Re{Z _(P1ON)*}  (2)

[0042] The greater the difference between Re{Za} and Re{Z_(P1ON)*}, thehigher the effect. If Re{Za} is five times or more Re{Z_(P1ON)*}, andmore preferably if the former is ten times or more the latter, thegreater part of the high-frequency power of the output signal of the f1amplifier element 17 can be output as the output signal Vo1.

[0043]FIG. 3 shows the impedances of the components of FIG. 1A assumedwhen the input signal Vi2 of the frequency f2 is input to the inputterminal 12, and the f2 amplifier element 18 is operating and the f1amplifier element 17 is not operating. The operating amplifier element18 has the output impedance Z_(P2ON). The first main electrode (outputterminal) of the amplifier element 18 is connected to the outputmatching circuit 22 having the conjugate impedance Z_(P2ON)* withrespect to Z_(P2ON), and is also connected to the power supply circuit.In the power supply circuit, DC power is supplied to the f2 amplifierelement 18 from the input-terminal 30 via the common power supply path31 and individual power supply path 33.

[0044] On the other hand, the f1 amplifier element 17, which is notoperating, has an output impedance Z6. The impedance Z7 of the outputmatching circuit 21 connected to the first main electrode (outputterminal) of the amplifier element 17 is identical to the conjugateimpedance Z_(P1ON)* with respect to the output impedance Z_(P1ON) Of theamplifier element 17 during operation.

[0045] Assuming that the synthesis impedance when the power supplycircuit is viewed from the first main electrode of the operating f2amplifier element 18 is Zb, Zb is given by $\begin{matrix}{Z_{b} = \frac{{Z_{1}\left( {Z_{2} + \frac{Z_{6}Z_{7}}{Z_{6} + Z_{7}}} \right)} + Z_{3}}{Z_{3}\left( {Z_{1} + Z_{2} + \frac{Z_{6}Z_{7}}{Z_{6} + Z_{7}}} \right)}} & (3)\end{matrix}$

[0046] In equation (3) directed to the case where the input signal Vi2of the frequency f2 is input to the input terminal 12, and the f2amplifier element 18 is operating, Z1, Z2 and Z3 in the equation (3) areZ1(f2), Z2(f2) and Z3(f2), respectively.

[0047] At this time, if the real part Re{Zb} of the synthesis impedanceZb is set higher than the real part Re{Z_(P2ON)*} of the impedanceZ_(P2ON)* of the output matching circuit 22, as shown in the followingformula (4), the output signal (high frequency power) of the amplifierelement 18 is efficiently guided to the output side via the outputmatching circuit 22, and output as the output signal Vo2.

Re{Z _(b) }>Re{Z _(P2ON)*}  (4)

[0048] Also in this case, if Re{Zb} is five times or more Re{Z_(P2ON)*},and more preferably if the former is ten times or more the latter, thegreater part of the high-frequency power of the output signal of the f2amplifier element 18 can be output as the output signal Vo2.

[0049] From the above formulas (1) to (4), Z1, Z2 and Z3 are determined.

[0050] As described above, the power supply circuit for supplying powerto the amplifier elements 17 and 18 comprises the common power supplypath 31 commonly provided for the amplifier elements 17 and 18, and theindividual power supply paths 32 and 33 provided for the amplifierelements 17 and 18, respectively, and having different impedances. Byvirtue of this structure, the power amplifier can be made compact.

[0051] The advantage of the above structure will now be described.Assume that the area of the common power supply path 31 is S1, and thoseof the individual power supply paths 32 and 33 are S2 and S3,respectively. In a power amplifier having a single amplifier elementoperable at a single frequency, the power supply circuit needs an areaof (S1+S2) or (S1+S3) (i.e., the sum of the area S1 of the common powersupply path and one of the areas S2 and S3 of the individual powersupply paths). Accordingly, where two individual power supply circuitsare provided for two amplifier elements, an area of (2S1+S2+S3) isneeded.

[0052] On the other hand, the area of the power supply circuit employedin the embodiment is (S1+S2+S3), which is smaller by S1 than the casewhere individual power supply circuits are provided for two amplifierelements. Since, in general, the power supply circuit occupies arelatively large area in the power amplifier, reduction of the area ofthe power supply circuit significantly contributes to the reduction ofthe size of the power amplifier.

[0053] In the embodiment, the output matching circuits 21 and 22 are setto have conjugate impedances with respect to the output impedances ofthe amplifier elements 17 and 18 during operation, respectively.However, the impedances of the circuits 21 and 22 are not limited to theconjugate ones, but may be varied in accordance with purposes.

SECOND EMBODIMENT

[0054] The power amplifier of the first embodiment is operable at twofrequencies f 1 and f2. However, a power amplifier that is operable atthree or more frequencies can be realized. In this case, it issufficient if the power amplifier comprises three or more amplifierelements, a single common power supply path, three or more individualpower supply paths and three or more output matching circuits. FIG. 4shows a power amplifier according to a second embodiment, which isoperable at three frequencies f1, f2 and f3. In FIGS. 4 and 5, elementssimilar to those in FIG. 1A are denoted by corresponding referencenumerals.

[0055] The second embodiment employs a f3 amplifier element 19, as wellas the f1 and f2 amplifier elements 17 and 18. DC power input to thepower supply input terminal is supplied to one end of the common powersupply path 31. After that, the DC power is distributed to the f1amplifier element 17 via the individual power supply path 32, to the f2amplifier element 18 via the individual power supply path 33, and to thef3 amplifier element 19 via the individual power supply path 34. Theindividual power supply paths 32, 33 and 34 have different impedances,as will be described later.

[0056]FIG. 5 shows the impedances of the components of FIG. 4 assumedwhen an input signal Vi3 of a frequency f3 is input to an input terminal13, and the f1 and f2 amplifier elements 17 and 18 are not operating andthe f3 amplifier element 19 is operating. The operating amplifierelement 19 has an output impedance Z_(P3ON). The first main electrode(output terminal) of the amplifier element 19 is connected to an outputmatching circuit 23 having a conjugate impedance Z_(P3ON)* with respectto Z_(P3ON), and is also connected to the power supply circuit.

[0057] On the other hand, the f1 amplifier element 17, which is notoperating, has an output impedance Z6. The impedance Z7 of the outputmatching circuit 21 connected to the first main electrode (outputterminal) of the amplifier element 17 is identical to the conjugateimpedance Z_(P1ON)* with respect to the output impedance Z_(P1ON) of theamplifier element 17 during operation. Similarly, the f2 amplifierelement 18, which is not operating, has an output impedance Z4. Theimpedance Z5 of the output matching circuit 22 connected to the firstmain electrode (output terminal) of the amplifier element 18 isidentical to the conjugate impedance Z_(P2ON)* with respect to theoutput impedance Z_(P2ON) Of the amplifier element 18 during operation.

[0058] Assuming that the synthesis impedance when the power supplycircuit is viewed from the first main electrode of the operating f3amplifier element 19 is Zc, Zc is given by $\begin{matrix}{Z_{c} = {Z_{8} + \frac{{Z_{1}\left( {Z_{3} + \frac{Z_{4}Z_{5}}{Z_{4} + Z_{5}}} \right)}\left( {Z_{2} + \frac{Z_{6}Z_{7}}{Z_{6} + Z_{7}}} \right)}{\begin{matrix}{{\left( {Z_{3} + \frac{Z_{4}Z_{5}}{Z_{4} + Z_{5}}} \right)\left( {Z_{2} + \frac{Z_{6}Z_{7}}{Z_{6} + Z_{7}}} \right)} + Z_{1} +} \\{\quad {\left( {Z_{3} + \frac{Z_{4}Z_{5}}{Z_{4} + Z_{5}}} \right) + {Z_{1}\left( {Z_{2} + \frac{Z_{6}Z_{7}}{Z_{6} + Z_{7}}} \right)}}\quad}\end{matrix}}}} & (5)\end{matrix}$

[0059] In equation (5) directed to the case where the input signal Vi3of the frequency f3 is input to the input terminal 13, and the f3amplifier element 19 is operating, Z1, Z2 and Z3 are Z1(f3), Z2(f3) andZ3(f3), respectively.

[0060] Similarly, the synthesis impedance Za, obtained if the powersupply circuit is viewed from the first main electrode of the f1amplifier element 17 when the element 17 is operating and the elements18 and 19 are not operating, is given by the following equation (6). Thesynthesis impedance Zb, obtained if the power supply circuit is viewedfrom the first main electrode of the f2 amplifier element 18 when theelement 18 is operating and the elements 17 and 19 are not operating, isgiven by the following equation (7). $\begin{matrix}{Z_{a} = {Z_{2} + \frac{{Z_{1}\left( {Z_{3} + \frac{Z_{4}Z_{5}}{Z_{4} + Z_{5}}} \right)}\left( {Z_{8} + \frac{Z_{9}Z_{10}}{Z_{9} + Z_{10}}} \right)}{\begin{matrix}{{\left( {Z_{3} + \frac{Z_{4}Z_{5}}{Z_{4} + Z_{5}}} \right)\left( {Z_{8} + \frac{Z_{9}Z_{10}}{Z_{9} + Z_{10}}} \right)} + Z_{1} +} \\{\quad {\left( {Z_{3} + \frac{Z_{4}Z_{5}}{Z_{4} + Z_{5}}} \right) + {Z_{1}\left( {Z_{8} + \frac{Z_{9}Z_{10}}{Z_{9} + Z_{10}}} \right)}}\quad}\end{matrix}}}} & (6) \\{Z_{b} = {Z_{3} + \frac{{Z_{1}\left( {Z_{2} + \frac{Z_{6}Z_{7}}{Z_{6} + Z_{7}}} \right)}\left( {Z_{8} + \frac{Z_{9}Z_{10}}{Z_{9} + Z_{10}}} \right)}{\begin{matrix}{{\left( {Z_{2} + \frac{Z_{6}Z_{7}}{Z_{6} + Z_{7}}} \right)\left( {Z_{8} + \frac{Z_{9}Z_{10}}{Z_{9} + Z_{10}}} \right)} + Z_{1} +} \\{\quad {\left( {Z_{2} + \frac{Z_{6}Z_{7}}{Z_{6} + Z_{7}}} \right) + {Z_{1}\left( {Z_{8} + \frac{Z_{9}Z_{10}}{Z_{9} + Z_{10}}} \right)}}\quad}\end{matrix}}}} & (7)\end{matrix}$

[0061] In equation (6) directed to the case where the input signal Vi1of the frequency f1 is input to the input terminal 11, and the f1amplifier element 17 is operating, Z1, Z2 and Z3 are Z1(f1), Z2(f1) andZ3(f1), respectively. Similarly, in equation (7) directed to the casewhere the input signal Vi2 of the frequency f2 is input to the inputterminal 12, and the f2 amplifier element 18 is operating, Z1, Z2 and Z3are Z1(f2), Z2(f2) and Z3(f2), respectively.

[0062] In those cases, if the real parts Re{Za}, Re{Zb} and Re{Zc} ofthe synthesis impedances Za, Zb and Zc are set higher than the realparts Re{Z_(P1ON)*}, Re{Z_(P2ON)*} and Re{Z_(P3ON)*} of the impedancesZ_(P1ON)*, Z_(P2ON)* and Z_(P3ON)* of the output matching circuits 21,22 and 23, respectively, as shown in the following formulas (8), (9) and(10), the output signals (high frequency power) of the amplifierelements 17, 18 and 19 are efficiently guided to the output side via theoutput matching circuits 21, 22 and 23, and output as the output signalsVo1, Vo2 and Vo3, respectively.

Re{Z _(a) }>Re{Z _(P1ON)*}  (8)

Re{Z _(b) }>Re{Z _(P2ON)*}  (9)

Re{Z _(c) }>Re═Z _(P3ON)*}  (10)

[0063] From the formulas (1) to (10), Z1, Z2 and Z3 are determined. Evenin the case of a power amplifier including four or more amplifierelements, the impedances of the common power supply path and individualpower supply paths can be determined by executing the same procedure asthe above.

[0064] Moreover, as in the first embodiment, if the real parts Re{Za},Re(Zb) and Re(Zc) of the synthesis impedances Za, Zb and Zc are fivetimes or more Re{Z_(P1ON)*}, Re{Z_(P3ON)*} and Re{Z_(P2ON)*},respectively, and more preferably if the formers are ten times or morethe latters, the greater part of the high-frequency power of the outputsignals of the f1, f2 and f3 amplifier elements 17, 18 and 19 can beoutput as the output signals Vo1, Vo2 and Vo3.

[0065] A description will be given of more specific power amplifierexamples according to the first and second embodiments.

[0066]FIG. 6 shows a first example of the power amplifier of the firstembodiment that is operable at the frequencies f1 and f2. In thisexample, the power supply circuit is formed of a plurality of spiralinductors. A spiral inductor 41 corresponds to the common power supplypath 31, and spiral inductors 42 and 43 correspond to the individualpower supply paths 32 and 33, respectively. The impedances of the spiralinductors 41, 42 and 43 are given by

Z ₁ =R ₁ +jωX ₁   (11)

Z ₂ =R ₂ +jωX ₂   (12)

Z ₃ =R ₃ +jωX ₃   (13)

[0067] where R1, R2 and R3 represent the resistance components, and X1,X2 and X3 the reactance components. R1, R2, R3, X1, X2 and X3 can bedetermined by combining the equations (11), (12) and (13) with theformulas (1), (2), (3) and (4), and setting an appropriate frequency.

[0068]FIG. 7 shows a second example of the power amplifier of the firstembodiment. In this example, the power supply circuit is formed ofmeander lines and capacitors. A meander line 51 corresponds to thecommon power supply path 31, and meander lines 52 and 53 correspond tothe individual power supply paths 32 and 33, respectively. Capacitors54, 55 and 56 are provided between the input terminals of the meanderlines 51, 52 and 53 and the earth, respectively.

[0069]FIG. 8 shows a third example of the power amplifier of the firstembodiment. In this example, the power supply circuit is formed oftransmission lines and bonding wires. A straight transmission line 61A,T-shaped transmission line 61B and boding wire 64 connecting themprovide a common power supply path corresponding to the common powersupply path 31 in FIG. 1A. The T-shaped transmission line 61B,transmission line 62 and boding wire 65 connecting them provide anindividual power supply path corresponding to the individual powersupply path 32 in FIG. 1A. Similarly, the T-shaped transmission line61B, transmission line 63 and boding wire 66 connecting them provide anindividual power supply path corresponding to the individual powersupply path 33 in FIG. 1A. Desired impedances can be obtained bychanging the lengths and/or thicknesses of the bonding wires 64, 65 and66.

[0070]FIG. 9 shows a fourth example of the power amplifier of the firstembodiment. In this example, the power supply circuit is formed of chipcomponents that include capacitors and inductors. A capacitor 71 andinductor 72 provide a common power supply path corresponding to thecommon power supply path 31 in FIG. 1A. A capacitor 73 and inductor 74provide an individual power supply path corresponding to the individualpower supply path 32 in FIG. 1A, while a capacitor 75 and inductor 76provide an individual power supply path corresponding to the individualpower supply path 33 in FIG. 1A.

[0071]FIG. 10 shows a fifth example of the power amplifier of the firstembodiment. In this example, the power supply circuit is formed ofinductors or median lines using via holes. Specifically, wiring layers81 and 82 on the upper and lower surfaces of a plate 80 called a moduleplate, respectively. Each of the wiring layers 81 and 82 has atransmission line 83 of a predetermined pattern. The upper and lowersurfaces of the substrate 80 are connected to each other by via holes84, thereby forming inductors or median lines.

[0072] Also in the second to fifth examples, R1, R2, R3, X1, X2 and X3can be determined by combining the equations (11), (12) and (13) withthe formulas (1), (2), (3) and (4), and setting an appropriatefrequency.

[0073]FIGS. 11A and 11B shows front and back structures of a sixthexample of the power amplifier of the first embodiment, respectively. Inthis example, the amplifier elements and power supply circuit areprovided on different layers of a multilayer substrate. Specifically,the f1 and f2 amplifier elements 17 and 18 and individual power supplypaths 32 and 33 are provided on the upper surface of a multilayersubstrate 90, while the common power supply path 31 is provided on thelower surface of the substrate 90.

THIRD EMBODIMENT

[0074]FIGS. 12A ,12B and 12C show, respectively, plural structures of apower amplifier according to a third embodiment that is operable at thefour frequencies f1, f2, f3 and f4. This power amplifier employs thestructure shown in FIG. 11A and 11B. Specifically, f1 and f2 amplifierelements 17 and 18 and individual power supply paths 22 and 23 areprovided on the upper surface 91 of a multilayer substrate. A commonpower supply path 21 is provided on the intermediate layer 92 of thesubstrate. Further, f3 and f4 amplifier elements 19 and 20 andindividual power supply paths 24 and 25 are provided on the lowersurface 93 of the substrate.

FOURTH EMBODIMENT

[0075]FIG. 13 shows a power amplifier according to a fourth embodimentof the invention. The power amplifiers of the first and secondembodiments have a single-stage structure, while the power amplifier ofthe fourth embodiment has a dual-stage structure.

[0076] In the fourth embodiment, input signals Vi1 and Vi2 offrequencies f1 and f2, supplied to input terminals 11 and 12, are inputto the first-stage f1 and f2 amplifier elements 17A and 18A via inputmatching circuits 14 and 15, respectively. The outputs of thefirst-stage f1 and f2 amplifier elements 17A and 18A are input to thesecond-stage f1 and f2 amplifier elements 17B and 18B via intermediatematching circuits 24 and 25, respectively. The outputs of thesecond-stage f1 and f2 amplifier elements 17B and 18B are extracted asoutput signals Vo1 and Vo2 via output matching circuits 21 and 22,respectively.

[0077] DC power is supplied to the first-stage f1 and f2 amplifierelements 17A and 18A via a first power supply circuit that has a commonpower supply path 31A and individual power supply paths 32A and 33A.Similarly, DC power is supplied to the second-stage f1 and f2 amplifierelements 17B and 18B via a second power supply circuit that has a commonpower supply path 31B and individual power supply paths 32B and 33B. Thefourth embodiment can be modified into a power amplifier including athree-stage or more structure.

FIFTH EMBODIMENT

[0078] A description will be given of a radio communication deviceaccording to a fifth embodiment of the invention, in which the poweramplifier of the first embodiment is incorporated in the transmissionsystem of the device. FIG. 14 shows the configuration of a radiocommunication device operable at two frequency bands.

[0079] Firstly, the receiving system of the device will be described. AnRF reception signal received by an antenna 100 is guided to thereceiving system via a duplexer 101, and distributed into two receivingroutes by a switch 102 in accordance with its frequency. If the RFsignal is distributed into a first receiving route, it is guided to amixer 107 via a band-pass filter (OPF) 103 and low noise amplifier (LNA)105, and is subjected to frequency conversion based on a local signalfrom a local signal source 109, i.e., it is down-converted.

[0080] The output signal of the mixer 107 is simultaneously input to twomixers 112 and 113 via a band-pass filter 110. The mixers 112 and 113provide an orthogonal demodulator, receive orthogonal local signals froma local signal source 114, and convert the signals, supplied from theband-pass filter 110, into orthogonal reception baseband signals, i.e.,I and Q signals. The orthogonal reception baseband signals are input toa baseband processing unit 120, where they are reproduced as receiveddata.

[0081] A second receiving route is similar to the first one, andcomprises a band-pass filter 104, low noise amplifier 106, mixer 108,band-pass filter 108, mixers 115 and 116, and local signal source 117.The local signal source 117 generates local signals of a frequencydifferent from that of the local signals generated by the local signalsource 114.

[0082] The transmission system will now be described. The basebandprocessing unit 120 performs digital signal processing on transmissiondata, thereby generating orthogonal transmission baseband signals, i.e.,I and Q signals. The generated I/Q signals are input to one of thetransmission routes in accordance with their transmission frequency. Ifthe I/Q signals are input to a first transmission route, they aremultiplied, in mixers 121 and 122, by the respective orthogonal localsignals from a local signal source 123. The output signals of the mixers121 and 122 are added by an adder 127. The mixers 121 and 122 and adder127 form an orthogonal modulator.

[0083] The output signal of the adder 127 is guided to a mixer 129,where it is subjected to frequency conversion based on a local signalfrom a local signal line 131, i.e., it is up-converted. The outputsignal of the mixer 129 is supplied to a band-pass filter 132, where anunnecessary component is eliminated therefrom. After that, the resultantsignal is amplified by a power amplifier 134. The output signal of thepower amplifier 134 is guided to a switch 137 via a low-pass filter 135,and then to the antenna 100 via the duplexer 101. Thus, the signal isoutput as an electric wave from the antenna.

[0084] The other transmission route, i.e., a second route, is similar tothe first one, and comprises mixers 124 and 125 and adder 128 providingan orthogonal modulator, local signal source 126 for the orthogonalmodulator, mixers 129 and 130 and local signal line 131 forup-conversion, band-pass filter 133, power amplifier 134 and low-passfilter 136. The transmission frequency, i.e., the frequency of atransmission signal input to the power amplifier 134, differs from thatof the first transmission route.

[0085] If the power amplifier of the first embodiment is used as thepower amplifier 134, it can be commonly used for two transmissionroutes. This being so, the whole area required for the power amplifiercan be reduced compared to the case where respective power amplifiersare used for two transmission routes, which contributes to the reductionof the size and cost of the radio communication device. Further, a radiocommunication device having three or more frequencies can be realized bymodifying the configuration of FIG. 14.

[0086] Additional advantages and modifications will readily occur tothose skilled in the art. Therefore, the invention in its broaderaspects is not limited to the specific details and representativeembodiments shown and described herein. Accordingly, variousmodifications may be made without departing from the spirit or scope ofthe general inventive concept as defined by the appended claims andtheir equivalents.

What is claimed is:
 1. A power amplifier comprising: a first amplifierelement configured to amplify a first input signal of a first frequency,the first amplifier element including a first input terminal whichreceives the first input signal, and a first output terminal whichoutputs a first output signal obtained by amplifying the first inputsignal; a second amplifier element configured to amplify a second inputsignal of a second frequency, the second amplifier element including asecond input terminal which receives the second input signal, and asecond output terminal which outputs a signal obtained by amplifying thesecond input signal; a power supply input terminal connected to adirect-current power supply; a common power supply path including an endconnected to the power supply input terminal, and another end; a firstindividual power supply path including an end connected to the anotherend of the common power supply path, and another end connected to thefirst output terminal, the first individual power supply path having afirst impedance; and a second individual power supply path including anend connected to the another end of the common power supply path, andanother end connected to the second output terminal, the secondindividual power supply path having a second impedance.
 2. The poweramplifier according to claim 1, further comprising a multilayer wiringboard comprising a first layer provided with the first amplifier elementand the second amplifier element, and a second layer provided with thecommon power supply path and the first individual power supply path andthe second individual power supply path.
 3. The power amplifieraccording to claim 1, further comprising a multilayer wiring boardcomprising a first layer and a second layer, wherein the first amplifierelement and the second amplifier element are provided on the firstlayer, and the common power supply path, the first individual powersupply path and the second individual power supply paths are provided onthe first layer and the second layer.
 4. The power amplifier accordingto claim 1, further comprising a multilayer wiring board comprising afirst layer and a second layer, wherein the first amplifier element, thesecond amplifier element, the first individual power supply path and thesecond individual power supply path are provided on the first layer, andthe common power supply path is provided on the second layer.
 5. Thepower amplifier according to claim 1, wherein the first individual powersupply path and the second individual power supply path have differentlengths.
 6. The power amplifier according to claim 1, wherein the commonpower supply path, the first individual power supply path and the secondindividual power supply path each comprising an inductance element.
 7. Apower amplifier comprising: a first amplifier element configured toamplify a first input signal of a first frequency, the first amplifierelement including a first input terminal which receives the first inputsignal, and a first output terminal which outputs a first output signalobtained by amplifying the first input signal; a second amplifierelement configured to amplify a second input signal of a secondfrequency, the second amplifier element including a second inputterminal which receives the second input signal, and a second outputterminal which outputs a signal obtained by amplifying the second inputsignal; a power supply input terminal connected to a direct-currentpower supply; a common power supply path including an end connected tothe power supply input terminal, and another end; a first individualpower supply path including an end connected to the another end of thecommon power supply path, and another end connected to the first outputterminal, the first individual power supply path having a firstimpedance; a second individual power supply path including an endconnected to the another end of the common power supply path, andanother end connected to the second output terminal, the secondindividual power supply path having a second impedance; a first outputmatching circuit connected to the first output terminal of the firstamplifier element; and a second output matching circuit connected to thesecond output terminal of the second amplifier element.
 8. The poweramplifier according to claim 7, wherein: the first amplifier element andthe second amplifier element are controlled exclusively to operate thefirst amplifier element and the second amplifier element; and the commonpower supply path, the first individual power supply path and the secondindividual power supply path, the first output matching circuit andsecond output matching circuit have respective impedances, each of therespective impedances being set to a value so that a real part of asynthesis impedance viewed from one selected from the first amplifierelement and second amplifier element that is in operation, to acorresponding one selected from the first and second individual powersupply paths, is greater than a real part of a corresponding oneselected from the first output matching circuit and second outputmatching circuit.
 9. The power amplifier according to claim 7, whereineach of the first output matching circuit and the second output matchingcircuit has a conjugate impedance with respect to an impedance of acorresponding one in operation of the first amplifier element and thesecond amplifier element.
 10. The power amplifier according to claim 7,further comprising a multilayer wiring board including a first layerprovided with the first amplifier element and the second amplifierelement, and a second layer provided with the common power supply pathand the first individual power supply path and the second individualpower supply path.
 11. The power amplifier according to claim 7, furthercomprising a multilayer wiring board including first layer and secondlayer, wherein the first amplifier element and the second amplifierelement are provided on the first layer, and the common power supplypath and the first individual power supply path and the secondindividual power supply path are provided on the first layer and thesecond layer.
 12. The power amplifier according to claim 7, furthercomprising a multilayer wiring board including first layer and secondlayer, wherein the first amplifier element and the second amplifierelement and the first individual power supply path and the secondindividual power supply path are provided on the first layer, and thecommon power supply path is provided on the second layer.
 13. The poweramplifier according to claim 7, wherein the first individual powersupply path and the second individual power supply path have differentlengths.
 14. The power amplifier according to claim 7, wherein thecommon power supply path, the first individual power supply path and thesecond individual power supply path each include an inductance element.15. A radio communication device which performs data reception andtransmission using one frequency band selected from a plurality offrequency bands, comprising: a transmission signal generator whichgenerates a transmission signal of the one frequency band ; and thepower amplifier according to claim 1, the power amplifier receiving thetransmission signal as an input signal.
 16. A radio communication devicewhich performs data reception and transmission using one frequency bandselected from a plurality of frequency bands, comprising: a transmissionsignal generator which generates a transmission signal of the onefrequency band; and the power amplifier according to claim 7, the poweramplifier receiving the transmission signal as an input signal.